1. Field of the Invention
This invention relates generally to seals for valves. More particularly, it relates to valve seal designs which permit improved sealing effectiveness under the influence of fluid pressure acting upon the valve.
2. Description of the Prior Art
Heretofore, in valves having a pivotable valve closure member which includes a segment of a sphere as a sealing surface, e.g. butterfly or ball valves, it has been common to employ valve seals of many different configurations and materials. Typical of such prior art seals are the butterfly valve seals disclosed by Priese in U.S. Pat. No. 3,563,510, which are retained in a generally annular recess in the valve body and which deflect under the influence of fluid pressure differential applied across the valve in a closed position to force the seal into a "corner" formed by a wall of the annular valve body recess and the peripheral sealing surface of the valve disk. Another approach disclosed in U.S. Pat. No. 3,734,457 to Roos, has been to provide a valve seal ring which is of lesser inside diameter of the sealing surface of the valve closure element and which is partially restrained against radial stretching by a resilient metal hoop, whereby an interference fit is achieved between the seal and the disk resulting in compression of the seal and stretching of the hoop upon closing the disk. Still another prior art approach disclosed by Helman et al. in U.S. Pat. No. 3,608,861 and by Swain Canadian Pat. No. 695,037 has been to provide a seal member retained in a valve body recess and a rigid annular projection on the downstream side of the body recess which function as a fulcrum to limit flexure under the influence of fluid pressure to improve sealing effectiveness.
While these and other related approaches to butterfly and ball valve seal design have proven effective in some applications, nevertheless certain problems have been encountered. When a fluorinated hydrocarbon polymer has been employed as the seal material in prior art valves the tendency of such a material to cold-flow has resulted in leakage across such valves when closed. Moreover, valves employing prior art seal configurations have not always proven effective in bidirectional service, i.e. in applications in which the higher fluid pressure may be applied to either side of the valve. Further, such seals have been, for the most part, useful only within a limited temperature range.